In vs =, performance considerations

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In vs =, performance considerations

robolance

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Points: 403
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November 13, 2014 at 8:12 am

#292384

I am tuning a very long and slow running process.
Somewhere in the past I heard/saw a discussion about how indexes are handled when using an 'IN' vs. using '='.
For example:
SELECT This, That, Other FROM sometable
WHERE this in (1,2,3)
vs
SELECT This, That, Other FROM sometable
WHERE this = 1 OR this = 2 OR this = 3
Is there any difference? I am doing testing and finding very little if any. What oother considerations should I keep in mind?

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Luis Cazares SSC Guru Points: 183698 More actions · Answer 1

There's no difference. SQL Server will interpret them as the same query.

Luis C.
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robolance SSC-Addicted Points: 403 More actions · Answer 2

That's the way I am leaning. After reading a bit, it appears that SQL Server engine will try to optimize the order of the items in the 'IN' clause. This would be a specific use case that would make a large difference rarely.

Other than that, it all comes down to readability.

The query in question has a list of about 50 terms. My long term plan is to take these items into a table and use a join to get the same effect. They do change occasionally. Short term, I am trying to break this into modular parts and I want to really understand what is going on with each piece of the query.

So I will move on to the next piece of the query and see if I can find anything with more impact there.

I appreciate you input.

g.britton SSChampion Points: 13863 More actions · Answer 3

robolance (11/13/2014)
I am tuning a very long and slow running process.
Somewhere in the past I heard/saw a discussion about how indexes are handled when using an 'IN' vs. using '='.
For example:
SELECT This, That, Other FROM sometable
WHERE this in (1,2,3)
vs
SELECT This, That, Other FROM sometable
WHERE this = 1 OR this = 2 OR this = 3
Is there any difference? I am doing testing and finding very little if any. What oother considerations should I keep in mind?

Is column 'this' indexed? If not, SQL will need a table scan to find them. If the table is large....

Gerald Britton, Pluralsight courses

robolance SSC-Addicted Points: 403 More actions · Answer 4

Yes. Looking at the execution plan, it is using the index for both options.

Gazareth One Orange Chip Points: 27737 More actions · Answer 5

If you look at the execution plan, you'll see that SQL converts the IN list into multiple OR conditions, so there's no difference.